Various techniques exist for measuring the three-dimensional (3D) shape of a foot for the production of orthoses. The traditional technique generally involves forming a cast and mold of the foot in a non-weight-bearing condition. Despite having certain advantages in terms of simplicity and cost, the casting techniques can be relatively time consuming and labor intensive, which limit the number of patients that a practitioner can treat daily.
More recent techniques have relied on optical imaging techniques to acquire a 3D plantar foot shape, typically using a digital laser scanner. The image data can subsequently be used in a computer-aided design and manufacturing (CAD/CAM) system to fabricate a patient-specific orthosis. Optical imaging techniques can provide time and cost advantages over traditional casting and molding techniques and, depending on the intended application, can allow the 3D plantar image to be acquired in any of a non-weight-bearing, full-weight-bearing and semi-weight-bearing state, each having its own challenges and limitations.
For example, measurement techniques that acquire an image of the plantar surface with the foot in a non-weight-bearing state generally cannot account for the natural elongation and deformation of the foot that occur when weight is applied thereto, which can lead to unreliable measurements. Meanwhile, in a full-weight-bearing condition, the deformation imposed on the foot can become significant enough so as to negatively affect the reliability of the scanned image, notably the arch measurements. It can also be difficult to position the foot in a neutral position in a full-weight-bearing condition. A semi-weight-bearing condition can provide an intermediate and, in principle, more accurate configuration to acquire an image of the plantar surface, as this condition is often more representative of the natural elongation and deformation of the foot in the walking stance. However, acquiring a 3D plantar image with the entire length of the foot in a semi-weight-bearing state is not straightforward, as achieving proper soft tissue deformation requires careful positioning of the foot, which can prove challenging using existing techniques.
Accordingly, many challenges remain in the development of techniques for acquiring a 3D plantar image with the whole foot in a semi-weight-bearing condition, while also overcoming or at least alleviating some of the drawbacks of existing techniques.